Overall, 56% of the female researchers are involved in international collaboration as measured by co-authorship. The corresponding figure for men is 66%. Thus, our study shows that overall male researchers are more often involved in international collaboration than their female colleagues. However, as expected there are large differences across fields (Fig. 1). International collaboration is much more frequent in the natural sciences, medical and health sciences, and technology compared with humanities and social sciences, and this holds for both genders. In the humanities, fewer than one-third of the researchers have publications involving international collaboration. There are gender differences in all fields. The gap is largest in the social sciences where the proportion for men is 44% and for women is 36% for women. The gap is smallest in the humanities (the difference is 3 percentage point).
Interestingly, in all domains the gaps are smaller than 10 percentage points, which is the difference for the total/all fields. This is due to the fact that male and female researchers are unevenly distributed across fields (see Table 2), and there are relatively more women in fields where the collaboration rates are lower. Correspondingly, in the natural sciences, which have the highest collaboration rates, there are relatively more men than women, and 28% of male researchers are in this category compared with 18% of female researchers.
Figure 2 shows the corresponding figures using the proportions of publications involving international collaboration as the indicator. Overall, male researchers have 37% of their publications in collaboration with researchers in other countries, while the corresponding figure for female researchers is 32%. Gender differences are observed across all fields, but now the differences are reduced. The most evident reduction in gender gaps is observed in natural sciences, where a 7-percentage point higher share of men are involved in international collaboration (Fig. 1), while the share of the publications that involve international collaboration is just 2 percentage points higher for men (Fig. 2). The reduction can be explained by differences in the underlying collaboration patterns. Among the researchers who have collaborated internationally (i.e. have published at least one internationally co-authored paper), women on average have higher collaboration rates than men.
The analysed dataset also includes data at the level of disciplines. An overview of both measures for the largest disciplines can be found in Appendix Table 13. This table shows that there are notable variations in the proportions of international collaboration also within the various fields. For example, in the humanities these proportions are much higher in archaeology and conservation than in literature. In medical and health sciences, international collaboration is much less frequent in nursing than in most of the other disciplines. In the social sciences, anthropology and law have the lowest proportions and geography and economics have the highest. These variations can be explained by the differences in publication modes discussed in the introduction.
International collaboration is only one kind of collaboration. Collaboration more generally involves co-operation among two or more researchers, regardless of whether they are located at the same institution, at external national institutions, or at institutions in other countries. One might assume that the international collaboration dimension partly is influenced by the other dimensions. If male researchers tend to have more co-authors generally than female researchers have, then they might have access to a larger collaborative network and would thus have an increased likelihood of also having more international co-authors. In order to assess this question, we have analysed the average number of authors per publication for each individual (Tables 3 and 4). As expected, researchers involved in international collaboration (i.e. those who have published at least one internationally co-authored paper), tend to have a much higher number of co-authors per publication on average (7.2 authors, including the researcher in question) than those who have not collaborated internationally (2.7 authors, including the researcher) (Table 3). Interestingly, there are hardly any gender differences. For researchers who have not collaborated internationally, women have marginally higher numbers of co-authors on average than men, while the opposite is the case for researchers with international collaboration. Similarly, the issue was analysed according to the intensity of the international collaboration (Table 4). The analysis shows that there is a strong correlation between this intensity and number of co-authors. For example, researchers who have 0–10% of their publications in collaboration with colleagues in other countries have 2.7 authors per publication on average, while the corresponding figure for those with an international collaboration rate of 90–100% is 12.4 authors. This correlation holds for both genders, and overall there are small gender differences and no systematic patterns. In some categories, women have slightly higher numbers of authors than men, while the pattern is the opposite in other categories. In conclusion, this analysis does not support the assumption that men and women are different when it comes to co-authorship practices more generally.
The analysis so far has shown that gender differences in international collaboration are observed for the two different measures, albeit to various extents. These crude figures might, however, be contingent upon the gender composition by academic position and publication output. In order to assess this question, in Tables 5 and 6 we present the results split by field, gender, academic position, and publication volume simultaneously. Here figures are shown only for categories with more than 20 researchers. In Table 5 we report the percentage of men/women who have collaborated internationally (yes or no), while in Table 6 we report the average shares of publications with international co-authors.
Comparing academic fields, researchers in the humanities (32%) and social sciences (40%) have the lowest shares of international co-publications, while those in technology (65%), medical and health sciences (73%), and natural sciences (81%) are far more international (Table 5, right column). The same rank order is also found when comparing shares of publications that involve international co-authorship (Table 6). Here, the lowest share is found in the humanities (12%) and the highest in natural sciences (56%).
In both tables, there is a clear association between the publication volume and international collaboration. At the overall level, 37% of men with 1–2 publications have collaborated internationally, while the corresponding figure for women is 33% (Table 5). For the group with 3–9 publications, the figures are 66% and 63%, respectively, and for the group with 10 + publications the figures are 95% and 93%, respectively. Thus, a higher publication volume increases the probability for international collaboration. This is not surprising because this indicator requires only one publication with international co-authorship. For the other indicator there is a similar but weaker association (Table 6). Across the three productivity groups, the proportions increase from 31 to 50% for men and from 27 to 45% for women.
In most fields and productivity groups, shares of international collaboration are highest among men. There are (at the overall level, i.e. by fields not taking academic position into account) only three categories where women rank higher than men on both measures (Tables 5 and 6), namely researchers with 1–2 publications in the medical and health sciences, researchers with 3–9 publications in technology, and researchers with 10 + publications in the social sciences. There are also a few categories where the two indicators show deviating patterns and one gender has the highest proportion on one indicator and the lowest on the other.
The findings above have important implications for the interpretation of the aggregated figures presented in Figs. 1 and 2. As shown in Table 2, a larger part of the female researchers are found in the category of researchers with low productivity (1–2 publications) compared with men (overall 38% and 27%, receptively). At the same time, this group has the lowest proportions of international collaboration. Thus, some of the inequalities at aggregated levels can be explained by the different representations of genders across productivity groups. As an example, in the natural sciences overall, 76% of the female researchers have collaborated with researchers in other countries compared with 83% for male researchers (Fig. 1). In other words, there is a difference of 7 percentage points. However, when the issue is analysed at the level of productivity groups, men in the natural sciences overall have 1, 4, and 2 percentage points higher proportions than women in the three productivity groups (1–2, 3–9, and 10 + publications, respectively) (Table 5). This means that in all groups the difference is significantly smaller than the difference at the overall level.
When also taking academic position into account, the pattern becomes less clear. In Table 5, men have higher collaboration proportions than women in 20 of 31 categories based on combinations of fields, academic positions, and productivity intervals, while the opposite is the case in 10 categories. In Table 6, there are 15 categories where men rank above women, 14 categories where women rank above men, and 2 categories with no difference. There are also a few cases where the two indicators provide contradictory results (i.e. categories where one gender has the highest proportion on one indicator and the lowest on the other). In addition, the number of observations in each category varies significantly (Appendix Table 12). Accordingly, it might be difficult to interpret and draw conclusion based on these findings.
In order to analyse these findings further, a bivariate correlation analysis was carried out of the dependent and independent variables. Spearman’s rank-correlation coefficients (rho) were calculated because the data were not normally distributed (Table 7). As can be seen, there is a very weak correlation between gender and the two core indicators—engaging in international collaboration (yes/no) (Spearman’s rho = 0.10, significant at the 0.01 level) and the proportion of publications with international co-authorship (Spearman’s rho = 0.08, significant at the 0.01 level). In contrast, the two other variables of productivity interval and field show a stronger correlation with the indicators of international collaboration. Here the Spearman’s rho ranges from 0.27 to 0.44. Thus, these results indicate that international collaboration is more strongly associated with publication productivity and field rather than gender. There is no correlation between gender and average number of authors per publication (Spearman’s rho = 0.01). As expected there is a very strong correlation between productivity and the normalised number of publications.
As a next step, a regression analysis for each field was carried out. When we take academic position, productivity intervals, and average number of authors per publication into account and conduct regression analysis on each major field, we are able to determine whether men collaborate more internationally than their female colleagues do. Table 8 summarises the regression results of the indicator of researchers involved in international collaboration (i.e. if a researcher has or has not collaborated internationally, see Table 5). The table includes the numbers of observations, the adjusted regression coefficients, and the standardised coefficients for each of the variables—gender (men = 1, women = 0), position (professors, associated professors, and postdocs relative to PhD students), productivity intervals (relative to the less productive group of researchers), and average number of authors per publication. Because the dependent output variable is binominal (1 or 0 if the researcher has collaborated internationally or not), logistic regression analyses were conducted. Due to the large differences in the propensity to collaborate internationally across fields, we have not carried out this analysis on the overall level (all fields).
The analysis shows that the selected variables—gender, academic position, productivity, and average number of authors per publication—in total explain 25–35% of the variance. The figure is lowest for the social sciences (0.25) and highest for the natural sciences (0.35). International collaboration can therefore partly be explained by these variables.
The regression summary reveals that productivity is the most important variable in terms of international collaboration, while gender is the least important variable. For all fields, researchers who have published 3–9 articles collaborate more internationally than the less productive researchers, and the highly productive researchers have even higher figures. These results correspond with the findings in Table 5. As for academic position, the results are not completely consistent across fields. However, we find that the international collaboration rates of professors are statistically significant and higher than for PhD students in all fields except the humanities. Interestingly, the results show that gender is a statistically significant variable only in the natural sciences.
A similar regression analysis was also carried out for the indicator measuring the degree of collaboration, i.e. the share of publications with international co-authorship (see Table 6). Because the dependent variable in this case is continuous and not categorical, we used linear regression. Moreover, the variable was not normally distributed and thus was log-transformed. As a result of the log-transformation, the researchers without international collaboration (values of 0) were left out of the analysis. Thus, this analysis has important limitations but nevertheless provides interesting complementary results. The regression results are presented in Table 9 below. This analysis concerning gender shows results in line with those presented above. For none of the fields was gender a statistically significant variable.
In Table 10 we present GDCI values in all categories so that we can identify one unified expression of the gender inequality. In addition to GDCI values, we report size-adjusted GDCIs (summed to 100, where GDCIs are adjusted for sample size). This enables us to identify in which categories the origins of the gender equality can be found and the relative contribution of each category to the total inequality.
The first observation in Table 10 is that it is in the group of less productive researchers (1–2 publications) that we find the greatest source of gender inequality. In the two publication output groups that we consider the most important ones, the gender inequality is much higher among the most productive researchers (36% of the total size-adjusted GDCIs) compared to the middle group (3–9 publications, 23%). Second, gender differences are almost non-existent in the humanities where international collaboration is far less common compared to other fields. Among the most productive humanists (and social scientists, too), women are in fact more internationally collaborative than men, but the overall contribution to gender differences is just 0.45%. Third, in the natural sciences there are no gender differences among the most productive researchers. Although this field tends to be dominated by men, the publishing behaviour of female natural scientists does not deviate from men among the most prolific researchers. In the least productive group, male natural scientists are more collaborative, while women have a higher index in the mid-productivity group (3–9 publications). Fourth, in technology there are strong gender differences (in favour of men) among researchers with few publications. Fifth, and most notably, in medical and health sciences female researchers are more internationally collaborative among the least-productive researchers, but the two single most important contributors to gender differences are found here among the more productive researchers. Although GDCI values are higher in some other categories, these two categories contribute to the largest part of the gender inequality in favour of men (due to the high n). Despite the fact that women are equally or more internationally collaborative than men in several categories, the overall results show that men rank above women in all productivity categories.
In Table 11 we provide more detailed results where academic position is also added as an explanatory variable. This enables us to identify in which areas of research, for which type of positions, and at which productivity level gender differences are present. At first glance, it is clear that gender differences in international collaboration are very minor or not present in most categories. In the categories where women have higher GDCIs than men, the relative contribution to the total inequality tends to be small because the GDCIs in favour of women are often based on very small samples (often in combination with low GDCIs). If we arbitrarily choose a 5% size-adjusted GDCI as the threshold for significant gender inequality, there are only two categories (female postdocs in the natural sciences and associate professors in medical and health sciences with 1–2 publications) where women have a substantially higher size-adjusted international collaboration index than men. Among men, on the other hand, there are several such categories. The strongest contributions to men’s higher degree of international collaboration is found for PhD students in technology and in the medical and health sciences with 1–2 publications and professors in the medical and health sciences with 10 + publications. Male PhD students contribute to 11.5% of the total size-adjusted GDCIs in technology and to 9.6% of the total size-adjusted GDCIs in the medical and health sciences.